1. Field of the Invention
The present invention relates to a toothed sintered pulley for use in power transmitting systems in various apparatuses, and more particularly, to an improvement in toothed sintered pulley comprising a rim having a large number of teeth on its outer peripheral surface and lightening grooves at those portions of its inner peripheral surface which correspond to the individual teeth, a boss located radially inside of the rim, and a connection which connects the inner peripheral surface of the rim with an outer peripheral surface of the boss.
2. Description of the Prior Art
There is a conventionally known toothed pulley in the form of a pressed pulley made from a sheet metal.
For example, for a toothed pulley for driving a cam shaft of an engine, reductions in size and weight are required in correspondence to increases in rotation and output power of the engine. However, the prior art pressed pulley is capable of meeting the need for the reduction in weight, but spontaneously has a limit in production with regard to the reduction in size.
Thereupon, a toothed sintered pulley produced by use of a powdered metal technique has been developed to meet the demand for reduction in size. In this type of the pulley, a large number of lightening grooves are provided in the rim as described above in order to provide a reduction in weight, but under the present circumstances, it is desired to provide a further reduction in weight to reduce an inertia moment and to reduce a backlash noise generated by meshing of the pulley with a belt.
FIG. 6 illustrates a general arrangement of a cam shaft driving system in an engine 01, in which a toothed sintered pulley 03 is attached through a boss 011 to a cam shaft 02 cantilever-supported to the engine 01, and a timing belt 07 is wound around the toothed pulley 03 and a toothed pulley 06 mounted on a crank shaft 05.
In the above construction, if the cam shaft 02 flexes even somewhat due to a tensile force of the timing belt 07 during operation of the engine, the timing belt 07 is displaced toward an outer half 010a,of a rim 010 in the toothed sintered pulley 03, projecting from a connection 012 in one of axial directions away from the engine 01, and as a result, an excessive stress is produced in the outer half 010a due to the tensile force of the timing belt 07.
In this case, the rigidity of the outer half 010a is relatively low due to the large number of lightening grooves and hence, in order to sufficiently resist such stress, it is necessary to provide an increase in rigidity of the outer half 010a.